In this grant application, we are focusing on the physiological condition of anaphylaxis, which is a severe, systemic allergic reaction that occurs quickly upon exposure to an allergen. The incidence rate has increased dramatically to 49.8 people per 100,000, many of which are elderly with comorbid conditions such as cardiovascular disease. The studies proposed in this grant application are directly related to anaphylaxis as we are examining the biosynthetic pathways of eicosanoids and other lipid mediators. These bioactive lipids are well known to be involved in inflammatory pathways as well as mediating mast cell activation and degranulation during anaphylactic responses. The synthesis of eicosanoids begins with the initial rate-limiting step, the formation of arachidonic acid (AA) via group IVA cytosolic phospholipase A2 (cPLA2a). Ceramide-1- phosphate (C1P) is a bioactive sphingolipid and a direct activator of cPLA2a both in vitro and in cells. Mutagenesis of critical amino acids for C1P interaction in cPLA2a inhibited the ability of enzyme to translocate in response to several inflammatory agonists. Hence, the association of cPLA2a with C1P is a major regulatory event in the biosynthesis of bioactive lipid mediators (e.g. eicosanoids). To further our understanding of the physiological relevance of this lipid:protein interaction in vivo, our laboratory created a knockin mouse with the C1P interaction site of cPLA2a ablated. Our preliminary data has demonstrated some intriguing findings for this new genetic model of cPLA2a. For example, some phenotypes reported for the cPLA2a knockout mouse were not apparent in the cPLA2a knockin mouse (e.g. spontaneous abortion) [14], while other phenotypes were conferred to the cPLA2a knockin mouse such as resistance to passive systemic anaphylaxis. Based on these preliminary findings by our laboratory and inferences from the literature, we hypothesize that the cPLA2a knockin mouse is resistant to anaphylaxis due to loss of specific lipid mediators. We further hypothesize that though wild type mice have an increased anaphylactic phenotype as they age, the cPLA2a knockin mice will remain resistant. Our proposed experiments will explore this hypothesis in depth both ex vivo and in vivo with the hope of developing new therapeutics to combat this disease state in both young and aging populations.